Seperate Audio Into Multiple Channels

I recently bought an RCA “Y” jack adapter (shown here) from Best Buy to connect my 5.1 channel home theatre to my laptop. To my dismay, sound only comes out of the front-right speaker of my home theatre. (I thought it would come out of both front speakers.) I called Best Buy to see if a 3.5mm Mini-to-RCA Stereo audio cable (shown here) would allow sound to come out of 2 speakers. They said it does not depend on if the cable has both white and red plugs/jacks, but rather if my laptop’s sound card is capable of splitting audio into separate channels.Does my current setup have that capability?